Dairy product and method for preparing same

ABSTRACT

The invention relates to a method for preparing a dairy product, in which a medium comprising milk or a milk product is treated under aerobic conditions with a lactose-negative, food-technologically acceptable microorganism, and is then kept under anaerobic conditions for some time. Furthermore, the invention relates to a dairy product obtainable by this method.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority of Vermin et al., PCTApplication PCT/NL99/00569 filed on Sep. 14, 1999, and Vermin et al.,Netherlands Application Serial No. 1010096 filed on Sep. 15, 1998entitled “Dairy Product and Method for Preparing Same.”

AREA OF THE INVENTION

The invention relates to a method for preparing a dairy product and to adairy product obtainable by this process.

BACKGROUND OF THE INVENTION

In the course of years more and more different types of dairy productshave been developed. The consumer can choose among a wide range ofproducts, such as custard in all kinds of flavors, ice cream, yogurt andyogurt beverages, quark (curd cheese), Biogarde®, sour cream, whippedcream and créme fraîche.

A number of the available dairy products are so-called fermented dairyproducts. That is to say that in the preparation of these products afermentation step is carried out. In such a fermentation step theproduct is treated with microorganisms and/or enzyme systems whichconverts the lactose present in the product to a greater or lesserextent. Such fermentations yield, depending on the employedmicroorganism or mixtures of microorganisms and enzymes, a dairy producthaving a characteristic flavor and texture. Examples of fermented dairyproducts are yogurt, Biogarde®, Biomild®, quark and sour cream.

In order to give dairy products, both fermented and non-fermented, aspecific desired flavor, diverse additives are added. Many employedadditives are sweeteners, flavorings, aromatics and colorings. Inproducts such as custard, fruit yogurt and yogurt beverages, it isconventional to use artificial additives, fruit juices or plantextracts.

Of a number of dairy products the consumer wishes a natural variant. Bythis is meant a dairy product which owes its characteristic appearanceand flavor to the nature of the dairy product itself, without additivesbeing added. Dairy products of which in particular the availability ofnatural variants is expected are yogurt, quark, buttermilk and the like.

U.S. Pat. No. 4,675,193 discloses a two-step method for preparing aproduct having a cheese flavor. To this end, in the first step a flavordeveloping medium having a fat content between 0.5 and 50% (w/v) and aprotein content between 0.3 and 12% (w/v), for instance milk or whey, istreated with a lipase and/or protease source. This step is carried outunder aerobic conditions, after which the employed lipase and/orprotease source is deactivated. In a second step a fermentation with alactic acid producing microorganism is carried out.

As the lipase and/or protease source, non-pathogenic microorganisms arepreferably used, such as Penicillium roqueforti, Oidum lactis(Geotrichum candidum), Cladisporum butaryl, Micrococcus and Candidalipsolytica. Preferably, C. lipsolytica is used.

The treatment step in which the flavor developing medium is usedcomprises a fermentation in which the lipase and/or protease sourceacidifies the medium to a pH between 4.5 and 5.5, followed by adeactivation.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a dairy product which asregards texture corresponds to a known dairy product, such as yogurt orquark, but which has a different flavor and/or odor.

Surprisingly, it has been found that such dairy products can be preparedby bringing a specific aroma into the dairy product, which aroma isproduced by a specific aerobic microorganism which is kept underanaerobic conditions for some time. Preferably, a conventionalfermentation is carried out during this anaerobic period.

The invention relates to a method for preparing a dairy product in whicha medium comprising milk or a milk product is treated under aerobicconditions with a lactose-negative food-technologically acceptablemicroorganism.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It has been found that in a medium treated under aerobic conditions witha lactose-negative, food-technologically acceptable microorganism duringan anaerobic period there are formed characteristic aromas. The natureof the aroma can be adjusted by the choice of the microorganism withinthe class of lactose-negative, food-technologically acceptablemicroorganisms.

The aroma imparted according to the invention to a dairy productoriginates from a microorganism which hardly changes the startingmaterial for the dairy product to be prepared in the sense that lactoseis not converted. There is thus obtained a dairy product which asregards the texture is substantially equal to known variants of thedairy product prepared, but which has a completely new flavor and/orodor.

On the other hand, the use of a lactose-negative microorganism in thepreparation of a dairy product is known per se. In J. Dairy Sci., (1996)79:937-942, Kwak et al. describe a method in which a lactose-negativeyeast of the species Saccharomyces cerevisiae is used to stabilizekefir. Kefir is a traditional, Russian, fermented milk beveragecontaining a minor amount of alcohol and carbon dioxide. According toKwak et al. the lactose-negative microorganism is used to producealcohol in a preliminary phase under anaerobic conditions. After thispreliminary phase an acidification with lactic acid bacteria is carriedout.

The starting material for the method according to the invention is amedium comprising milk or a milk product. It is possible to use both anon-treated milk and a milk which has been subjected previously to aheat treatment, such as a pasteurization or sterilization.

In order to prevent outgrowth of any present, contaminatingmicroorganisms, it is preferred to start from a milk which has beenpreviously subjected to a heat treatment.

It is also possible to use a milk-derived product having an adapted fatcontent, such as skim milk or cream.

In addition to the milk or the milk product, the medium can and willgenerally comprise nutrients for the lactose-negative,food-technologically acceptable microorganism. It is conventional tosubdivide these nutrients into carbon sources and nitrogen sources.suitable carbon sources are substances which can supply the carbonrequired for the ripening of the lactose-negative, food-technologicallyacceptable microorganism, and which are compatible with the dairyproduct (to be prepared). Examples are glucose and potato dextrose broth(PDB). Suitable nitrogen sources are substances which can supply thenitrogen required for the ripening of the lactose-negative,food-technologically acceptable microorganism and have no negativeeffect on the dairy product (to be prepared). Examples are malt extract,yeast extract and tryptone.

The choice of the nutrients to be used will depend on the nature of thelactose-negative, food-technologically acceptable microorganism. Whenthe lactose-negative, food-technologically acceptable microorganism is ayeast, glucose, PDB and tryptone are preferably used as nutrients. Whenthe lactose-negative, food-technologically acceptable microorganism is abacterium, glucose and/or tryptone are preferably used as nutrients.

The amounts of the nutrients in the medium which form the startingmaterial for a method according to the invention are adjusted to thenature of the lactose-negative, food-technologically acceptablemicroorganism. The total amount of added nutrients required for thearoma-forming microorganism should be sufficient to grow themicroorganism, but not so large as to bring about an undesired aroma oran aroma of an undesired intensity. When the carbon source is PDB, inthe case that the lactose-negative, food-technologically acceptablemicroorganism is a yeast, the amount thereof will range between 1 and 3g. When in the same case tryptone is the nitrogen source, 0.2 to 1 gthereof will be used. When the carbon source is glucose, in the casethat the lactose-negative, food-technologically acceptable microorganismis a bacterium, the amount thereof will range between 0.5 and 5 g. Whenin the same case tryptone is the nitrogen source, 0.2 to 1 g thereofwill be used. All this can be simply established by those skilled in theart by way of experiment.

The microorganism with which the medium according to the invention istreated is a lactose-negative, food-technologically acceptablemicroorganism. By this is meant a microorganism which is not capable ofconverting lactose. In other words, when only lactose is present as thecarbon source, the microorganism cannot grow.

Preferably, the lactose-negative, food-technologically acceptablemicroorganism is a yeast or a bacterium. Very suitable yeast strains areCandida zelanoides CBS 2328, Candida zelanoides ATCC 26318, Debaryomyceshansenii CBS 772, Debaryomyces hansenii ATCC 10623, Saccharomycescerevisiae CBS 400, Saccharomyces cerevisiae CBS 437, Candida robustaCBS 420 and Zygosaccharomyces rouxii CBS 441. Very suitable bacteriaoriginate from the strains Micrococcus luteus ATCC 4698, Micrococcusluteus CIP A270, Arthrobacter nicotianea ATCC 21279 and Corynebacteriumflavescens ATCC 10340.

It is also possible to use combinations of lactose-negative,food-technologically acceptable microorganisms.

The choice of the lactose-negative, food-technologically acceptablemicroorganism or the combination of lactose-negative,food-technologically acceptable microorganisms can be suitably adjustedto the desired aroma. It has been found that by means of the treatmentwith the above microorganisms there can be produced a wide range ofaromas, including caramel, chocolate, cheesy, nutty, garlic, and aneutral aroma which, however, makes the flavor of the fermentationproduct richer and rounder.

In order to obtain the desired aroma, the medium comprising the milk orthe milk product is treated with the lactose-negative,food-technologically acceptable microorganism. This lactose-negative,food-technologically acceptable microorganism is added to the medium andripened. The amount of the lactose-negative, food-technologicallyacceptable microorganism can be suitably adjusted to the amount ofmedium and the amount (the strength) of the desired aroma. Thelactose-negative, food-technologically acceptable microorganism willgenerally be used in an amount of 10⁶ to 10⁷ per ml of milk or milkproduct.

The ripening of the lactose-negative, food-technologically acceptablemicroorganism is effected under aerobic conditions. The pH and thetemperature during the ripening will depend on the employed specificlactose-negative, food-technologically acceptable microorganism. In mostcases the pH will range between 6 and 7. The temperature will mostly bechosen between 25 and 30° C.

Preferably, the ripening is effected so as to be complete. The durationof the ripening depends on the W stationary growth phase of the employedmicroorganism; and will generally range between 12 and 24 hours. Thishas the result that the nutrients present in the medium are consumed andremainders of any nutrients added will hardly, if at all, find their wayinto the ready dairy product. The moment at which the ripening iscomplete, can be suitably determined by following the content of one ormore of the nutrients, for instance of glucose. It is also possible tofollow the growth of the lactose-negative, food-technologicallyacceptable microorganism by means of conventional plate counts.

After the ripening the resulting product is brought under anaerobicconditions for some time. It has been found that in the absence ofoxygen the aromas of the ripening strain are formed and are excellentlyexpressed.

During the aroma formation a neutral pH is preferably used. In mostcases a period of 5 to 12 hours will be sufficient to obtain a properaroma formation.

The thus obtained product is suitable per se for consumption. It will beclear that the formation of the desired aromas can take place forinstance after the dairy product has been packaged into a container inwhich conventional anaerobic conditions prevail. Often, however, theresulting product will be thermized to increase the keeping quality.Furthermore, depending on the desired nature of the dairy productprepared, additional operations can be carried out.

In a preferred embodiment the anaerobic conditions coincide with afermentation step. After addition of conventional fermentation strainsan anaerobic fermentation is carried out in which lactose is convertedinto, inter alia, lactic acid.

More in detail, the product obtained after the ripening of thelactose-negative, food-technologically acceptable microorganism istreated with a lactic acid bacterium. Because of this treatment, thedairy product, particularly as regards texture and acidity, will showgreat similarities to known fermented dairy products, such as yogurt orquark. On account of the change in the acidity in a treatment with alactic acid bacterium, this treatment is often designated asacidification.

The nature of the lactic acid bacterium will be suitably adjustable tothe desired product by those skilled in the art. The treatment with thelactic acid bacterium can be carried out in the known manner and will beanalogous to the treatment of a milk or milk product with a lactic acidbacterium in the preparation of fermented dairy products which have notbeen treated with a lactose-negative, food-technologically acceptablemicroorganism.

It will be clear that the invention also relates to a dairy product thatcan be prepared by a method as described above. Furthermore, theinvention relates to the use of a dairy product that can be preparedaccording to the invention in the preparation of automated products inthe food industry.

The invention will now be further explained on the basis of thefollowing examples.

EXAMPLE 1

Yeast strains:

Candida zelanoides CBS 2328 from ampoule

Candida zelanoides ATCC 26318 from ampoule

Debaryomyces hansenii ATCC 10623 from ampoule

Debaryomyces hansenii ATCC 772 from ampoule

Bacterial strain:

Arthrobacter nicotianea ATCC 21279 from plate

Glucose solution:

8 g of glucose per 100 g of water (filter sterilized)

Yeast medium:

24 g of potato dextrose broth (PDB of Difco 0549-17-9)

+5 g of tryptone per liter of water.

Bacterial medium:

5 g of tryptone per 900 ml of water. Sterilized at 120° C. for 15 minand enriched with 100 ml of glucose solution

Substrate:

whole UHT-milk

Culture

A colony of lactose-negative microorganisms is added to water withglycerol and the solution is distributed over several ampoules andfrozen. Subsequently, 1 ml of thawed medium is added to 25 ml of yeastof bacterial medium in an Erlenmeyer of 100 ml. The Erlenmeyer is closedwith cellulose wadding and aerobically stored for 72 hours at 25° C.(yeasts) and 30° C. (bacteria) at a shaking speed of 200 rpm.

Pre-culture

5 ml of culture medium is added to 45 ml of whole UHT milk (substrate)in an Erlenmeyer of 250 ml which is closable with wadding. This solutionis aerobically stored for 24 hours or 12 hours with shaking at 200 rpmand at the right temperature. After the pre-culture has been finished,the media are cooled to ca. 7° C.

Result

After an aerobic growth of the lactose-negative, food-technologicallyacceptable yeast Candida zeylanoides and an anaerobic aroma formation inmilk, there is formed a product with a distinguishing flavor, to beassociated with Munster cheese (stable flavor). When the startingmaterial is lactose-negative bacterium Arthrobacter, a chocolate flavoris formed after an anaerobic aroma formation in milk. In this productbranched chain aldehydes were the most important compounds that could bedetected with “dynamic headspace GCMS”.

EXAMPLE 2

Yeast strains:

Candida zelanoides CBS 2328 from ampoule

Candida zelanoides ATCC 26318 from ampoule

Bacterial strain:

Arthrobacter nicotianea ATCC 21279 from plate

Lactic acid bacteria:

For the preparation of yogurt

Glucose solution:

8 g of glucose per 100 g of water (filter sterilized)

Yeast medium:

24 g of potato dextrose broth (PDB of Difco 0549-17-9) +5 g of tryptoneper 1 of water.

Bacterial medium:

5 g of tryptone per 900 ml of water. Sterilized at 120° C. for 15 minand enriched with 100 ml of glucose solution

Substrate:

whole UHT-milk

Culture

A colony of lactose-negative microorganism is added to water withglycerol and the solution is further distributed over several ampoulesand frozen. Subsequently, 1 ml of thawed medium is added to 25 ml ofyeast or bacterial medium in an Erlenmeyer of 100 ml. The Erlenmeyer isclosed with cellulose wadding and aerobically stored for 72 hours at 25°C. (yeasts) and 30° C. (bacteria) at a shaking speed of 200 rpm.

Pre-culture

5 ml of culture medium is added to 45 ml of whole UHT milk (substrate)in an Erlenmeyer of 250 ml which is closable with wadding. This solutionis aerobically stored for 24 hours or 12 hours with shaking at 200 rpmand at the right temperature. After the pre-culture has been finished,the media are cooled to ca. 7° C.

Acidification

The pre-culture is acidified under anaerobic conditions with a yogurtculture at 37° C. to final pH 4.5 and further packaged in cooledcondition (to ca. 5-7° C.).

Result

when both products obtained in Example I are acidified with lactic acidbacteria, there are formed products having a consistency comparable tothat of yogurt and having a distinguishing flavor clearly different fromthe flavor of a non-pretreated, acidified milk product.

What is claimed is:
 1. A method for preparing a dairy product comprisingthe steps of: (a) adding a lactose-negative, food-technologicallyacceptable microorganism to a medium comprising milk or a milk product;(b) ripening said microorganism under aerobic conditions; and (c)bringing the resulting product under anaerobic conditions such as tohave aromas of the ripening microorganism formed.
 2. The methodaccording to claim 1, in which the microorganism is a yeast.
 3. Themethod according to claim 2, in which the yeast originates from one ofthe following set of strains: Candida zelanoides, Debaryomyces hanseniispp hansenii, Saccharomyces cerevisiae, Candida robusta, orZygosaccharomyces rouxii.
 4. The method according to claim 1, in whichthe medium is treated under anaerobic conditions with afood-technologically acceptable lactic acid bacterium.
 5. The methodaccording to claim 1 in which the milk or milk product is sterilized. 6.A dairy product prepared by treating a medium comprising milk or a milkproduct under aerobic conditions with a lactose-negative,food-technologically acceptable microorganism to render a treated mediumcomprising milk or a milk product; and maintaining the treated mediumcomprising milk or a milk product under anaerobic conditions.
 7. Amethod for producing a food comprising a dairy product comprising:introducing a lactose-negative, food-technologically acceptablemicroorganism to a medium comprising milk or a milk product, therebyimparting an aroma to the dairy product.
 8. The method according toclaim 6 further comprising preparing an aromatized food productincluding the dairy product.
 9. The method according to claim 1, inwhich the microorganism is a bacterium.
 10. The method of claim 2wherein the milk or milk product is sterilized.
 11. The method of claim3 wherein the milk or milk product is sterilized.
 12. The method ofclaim 4 wherein the milk or milk product is sterilized.
 13. The dairyproduct according to claim 6, in which the microorganism is a yeast. 14.The dairy product according to claim 13, in which the yeast originatesfrom one of the following set of strains: Candida zelanoides,Debaryomyces hansenii spp hansenii, Saccharomyces cerevisiae, Candidarobusta, or Zygosaccharomyces rouxii.
 15. The dairy product according toclaim 6, in which the microorganism is a bacterium.
 16. The methodaccording to claim 15, in which the bacterium originates from one of thefollowing set of strains: Micrococcus luteus, Arthrobacter,Corynebacterium or Arthrobacter ssp.
 17. The method according to claim6, in which the medium is treated under anaerobic conditions with afood-technologically acceptable lactic acid bacterium.
 18. The methodaccording to claim 6 in which the milk or milk product is sterilized.19. The method according to claim 9, in which the bacterium originatesfrom one of the following set of strains: Micrococcus luteus,Arthrobacter, Corynebacter or Arthrobacter ssp.